Light scattering by colloidal

Describes theory of light scattering by colloidal particles. 

Another microscopy technique, which is actually based on light scattered by colloids, is dark-field or ultra-microscopy. In this technique, an ordinary optical microscope is used, but the sample is illuminated in such a way that light does not enter the objective unless scattered by the object under investigation. This technique does now allow a direct observation of, for example, a particle, but is particularly useful for detecting the presence of particles and investigating the Brownian motion of colloids. An important requirement is that the refractive index of the coUoids... 

Debye, P. (1947) Molecular-weight determination by light scattering./. Phys. Colloid Chem. 51, 18-32. 

Finsey R., Particle sizing by quasi-elastic light scattering, Adv. Colloid Interface Set, 52, 79, 1994. 

Thomas J.C., The determination of log normal particle size distributions by dynamic light scattering, J. Colloid Interface Sci., 117, 187, 1987. 

Since the micelles are of colloidal dimensions, they are capable of scattering light and the white colour of milk is due largely to light scattering by the casein micelles the white colour is lost if the micelles are disrupted, e.g. by removing colloidal calcium phosphate (by citrate, ethylene... 

If the intensity of light scattered by a colloidal dispersion is measured as a function of c and 0, the Zimm method enables us to convert this information into several parameters that characterize the colloid M, B, and Rg. In some situations this is more information than is actually needed. If spatial extension is the only information sought, a simpler method for evaluating it employs the so-called dissymmetry ratio. 

These data can be used quantitatively as well as qualitatively to determine the molecular weight of the micelle. For example, the colloidal particles may be analyzed by light scattering by modifying Equation (5.39) as follows ... 

Practically, the phase delay (Or and the modulation ratio uir of the light scattered by a solution of glycogen or a suspension of colloidal silica are measured with respect to the signal detected by the reference photomultiplier. Then, after rotation of the turret, the phase delay and the modulation ratio mp for the sample fluorescence are measured with respect to the signal detected by the reference photomultiplier. The absolute phase shift and modulation ratio of the sample are then C> = (pp — and M = mp/mp, respectively. 

Hellweg, Th. and Eimer, W. (1998) The micro-structures formed by Ni2+ -AOT/ cyclohexane/water microemulsions A light scattering study. Colloids Surf. A, 136, 97-107. 

The above calculations refer to light scattered by a single particle. Provided that a colloidal dispersion is not too concentrated, the scattering is simply the sum of contributions from individual particles. Thus the intensity of light scattered at an angle 6 by unit volume of a dilute suspension of particle concentration c is... 

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